Note: Descriptions are shown in the official language in which they were submitted.
WO 800365-VB/LM/li CA 02577404 2007-02-16
0 9 -06e 2006
Joint prosthesis and method of bone fixation 9s
The invention relates to a joint prosthesis, for
example, a knee joint or shoulder joint prosthesis comprising
a first, socket-holding prosthesis part for attachment to a
first bone and a second, ball-holding prosthesis part for
attachment to a second bone that intermates with the first
prosthesis part, wherein the first bone and the second bone
are situated at either side of a joint, and wherein the ball
of the second prosthesis part is rotatably received in the
socket of the first prosthesis part.
Such a joint prosthesis is known in the form of a
shoulder joint prosthesis from the article 'Bipolar Shoulder
Arthroplasty for painful conditions of the Shoulder', by
Richard L. Warland and Jorge Aradondo, published in 'The
Journal of Arthroplasty' Vol. 13 No. 6 1998, pages 631 to
637.
Both from DE-C-41 33 433 and EP-A-0 628 294 hip
prostheses are known that comprise a socket-like part, and
each of which requires the prosthesis design-to precisely
match the anatomy of the patient.
Although the joint prosthesis according to the
invention isparticularly suitable to be applied as shoulder
joint prosthesis, the invention is not limited to this appli-
cation; it is also possible to create other joints with the
aid of the joint prosthesis of the invention. Nevertheless,
the invention will be elucidated by way of a shoulder joint
prosthesis. To the person skilled in the art it is completely
obvious how a corresponding operation needs to be performed
in, for example, a knee joint or hip joint.
Joint pathology that may result from fractures or
joint diseases such as rheumatoid arthritis and arthrosis may
seriously diminish the bone quality of the joint surfaces and
the stabilising effect of the surrounding tissue. The joint
becomes stiff and painful and will eventually cause chronic
pain and will seriously limit the activities of day-to-day
life. In order to alleviate the pain and to restore the
function of the joint, a total joint reconstruction may be
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performed. In a conventional joint replacement, both joint
surfaces are replaced by a metal ball in the upper arm (hume-
rus) and a polyethylene socket implanted in the shoulder
blade (glenoid fossa). Apart from alleviating the pain, the
object of this operation is the restoration of the joint
stability and the joint functionality. The postoperative
results of this procedure depend on, among other things, the
quality of the bone and of the surrounding capsule and muscle
tissue, on the medical history and age of the patient and on
the skill of the surgeon. The most prevalent postoperative
complications are instability of the joint and loosening of
the glenoid component.
In the case of rheumatoid arthritis there are two
important conflicting factors regarding the implantation of a
conventional shoulder prosthesis: (1) the lack of the me-
chanical bone quality necessary for a durable attachment, (2)
the loss of the function of surrounding muscles and ligaments
of the shoulder, which reduces the necessary joint compres-
sion required for stabilising the joint.
From the above-mentioned prior art the use of a so-
called bipolar prosthesis is known. This prosthesis consists
of a metal ball that articulates in a conforming synthetic
dish. The dish is placed without fixing into a steel shell
that is placed against the shoulder blade. The metal ball is
placed into the humerus (upper arm). This prosthesis ensures
sufficient rotation of the upper arm in relation to the
torso, with less wear of the underlying bone. However, the
prior art is unable to guarantee stability of the joint.
It is the object of the invention to eliminate this
problem and to gain advantages that will be clarified herein-
after.
EP-A-0 314 951 teaches a joint prosthesis, for
example, a knee jointor shoulder joint prosthesis comprising
a first, socket-holding prosthesis part for attachment to a
first bone and a second, ball-holding prosthesis part for
attachment to a second bone that intermates with the first
prosthesis part, wherein the first bone and the second bone
are situated at either side of a joint, and wherein the ball
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of the second prosthesis part is rotatably received in the
socket of the first prosthesis part, and further comprising
rods having a tensile strain bearing capacity for coupling
the first prosthesis part with the first bone wherein the
rods extend through openings in the first prosthesis part and
are each designed to project through a drilling in the first
bone, and are provided with an enlarged end at the side
facing away from the first prosthesis part.
The joint prosthesis of the invention is character-
ised in that said rods are provided with a locking element
formed like a sleeve with an inside diameter that is smaller
than the diameter of the enlarged end, which sleeve is mov-
able around the rods and forms a closed ring, which is pro-
vided with anchor arms that in a first position extend along
the rods, and being adjustable to a second position, in which
said anchor arms have a substantially radial orientation in
relation to the rods.
One thing and another makes it possible for the
prosthesis according to the invention to be implanted and
fastened by means of a one-sided operation. In such a case
the operation can then be of a minimally invasive nature.
With the prosthesis of the invention it is possible
to fasten the prosthesis in the first bone such as to provide.
an anchoring of sufficient strength and of a durable nature,
also in the case of rheumatoid arthritis.
The rods form artificial ligaments and through
translation of the upper arm in any arbitrary direction, they
draw the first prosthesis portion against the shoulder blade
in such a way as to provide a stabilised power-retaining
system.
In a preferred embodiment, the rods divert in the
mounted situation preferably in such a manner as to approxi-
mately create a virtual point of intersection, which substan-
tially coincides with a stationary point of rotation of the
ball of the second prosthesis part in the socket of the first
prosthesis part.
As the lines of force in the artificial ligaments
formed by the rods coincide with the point of rotation of the
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second prosthesis part, the forces exerted on the prosthesis
do not cause it to rotate.
The stability of the joint prosthesis is enhanced by
applying at least three rods having a tensile strain bearing
capacity.
To serve convenience and simplicity when implanting
the prosthesis, each of the rods is provided with thread so
that an insert nut can be fitted in a socket of the first
prosthesis part.
It is worth noting that fastening the prosthesis by
using these rods prevents said artificial ligaments from
coming under strain of bending. These rods should only absorb
tensile forces. This helps to extend the mechanical life of
the prosthesis and avoids post-operative complications.
An above-mentioned embodiment of the locking element
to be used for bone fixation is designed like a sleeve that
forms a closed ring provided with anchor arms, which in a
first position are oriented parallel to the axis of the
sleeve body, and being adjustable to a second position in
which the anchor arms extend substantially radially from the
sleeve.
With this locking element a new method of bone
fixation can.be applied with which it is also possible to
repair bone fractures, and with which it is possible to
realise the above-elucidated advantages of tensile strain
tolerance in the absence of flexural strain, which would lead
to premature loosening of the connecting bone parts.
In this connection, the invention is also embodied
in a method of bone fixation, which is characterized in that
the bone is provided with at least one drilling, a draw rod
provided with an enlarged end is inserted through the drill-
ing, and a locking element is used that prevents the removal
of the draw rod from the drilling.
This may be realised, for example, by inserting the
locking element into the drilling to prevent the enlarged end
from passing through the drilling.
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Another possibility is to fit the locking element
onto the draw rod, so that the locking element is embodied in
accordance with claim 10.
The advantages of the invention particularly come
5 available when each draw rod is mounted such that when the
mounted prosthesis is in a virtually unloaded condition,
there is no significant tensile force in the rod.
It is further beneficial for the stability that the
rods are mounted so as to be free of stress of bending.
Hereinafter-the invention will be further elucidated
by way of a non-limiting exemplary embodiment and with refer-
ence to the drawing.
The drawing shows in:
- Fig. 1, an exploded view of the joint prosthesis
according to the invention such as can be used as shoulder
joint prosthesis;
- Fig. 2, the joint prosthesis shown in Fig. 1 in
the mounted situation;
- Fig. 3, the joint prosthesis according to the
invention in an exploded view;
- Fig. 4, the locking element that serves for mount-
ing the joint prosthesis in the pre-mounted and in the
mounted situation.
Similar parts in the figures carry identical refer-
ence numerals.
In Fig. 1, the joint prosthesis is indicated with
reference numeral 10. This joint prosthesis 10 comprises a
first, socket-holding prosthesis part 11 for fastening to a
first bone 12, and a second, ball-holding prosthesis part 13
for fastening to a second bone 14, that intermates with the
first prosthesis part 11.
In the case shown, the first bone concerns the
shoulder blade.or the glenoid fossa 12, while the second bone
in the case shown is the upper arm or the humerus 14.
The second prosthesis part 13 comprises a ball 2
that is rotatably received in the socket 5 of the first
prosthesis part 11. This can be clearly understood from the
exploded view in Fig. 3,
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In accordance with the invention, the first prosthe-
sis part 11 can be coupled with the first bone 12 by using
three or four rods 6.having a tensile strain bearing capac-
ity.
Fig. 3 clearly shows that in the mounted situation,
the at least three rods 6 have a diverging orientation. The
divergence of the orientation should be such as to create
approximately a virtual point of intersection that substan-
tially coincides with a stationary rotational point of the
ball 2 of the second prosthesis part 13 in the socket 5 of
the first prosthesis part 11.
Fig. 2 shows the joint prosthesis in the mounted
situation. Viewing Fig. 2 in association with Fig. 3, shows
that the at least three rods 6 extend through openings in the
socket 5 of the first prosthesis part 11 and are designed to
project through a drilling in the first bone 12 and that at
the side of the bone 12 facing away from the socket 5, the
rods 6 are provided with locking elements 7.
Each of the just-mentioned locking elements 7 is
embodied as a sleeve 7, moveable on the artificial ligaments,
that is to say the rods 6, and forms a closed ring that in
the pre-mounted condition has a first position with anchor
arms extending along the rods 6. This is shown by the two
sleeves 7 on the left in Fig. 4. The inside diameter of the
sleeves 7 is smaller than the diameter of the enlarged end 15
of the rods 6 such that this end 15 forms an obstruction
preventing the sleeves 7 from sliding off.
The locking elements 7 can be brought into the
mounted situation, as shown in Fig. 2 and like the two
sleeves 7 shown on the right in Fig. 4, with the anchor arms
8 extending substantially radially in relation to the rods 6.
This is also clearly shown in Fig. 2.
An alternative manner of securing the rods 6 relates
to the use of a locking element in the form of a sleeve to be
inserted into the bone drillings and having an inside diame-
ter that is smaller than the diameter of the enlarged end 15
of the rods 6. Such sleeves have to be positioned after the
insertion of the rods 6. One thing and another is quite
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obvious to the person skilled in the art so that a further
elucidation by way of a figure is not necessary.
Fig. 3 shows that to fasten the rods 6, they can be
fixed at the inside of the socket 5 by means of an insert nut
4. To this end the rods 6 are preferably provided with an
external thread.
Finally, it is worth noting that in the completed
situation, the ball 2 of the second prosthesis part 13 is
placed in the socket 5 of the first prosthesis part 11, with
the ball 2 preferably being received in a polyethylene inner
socket 3. The position of the ball 2 is secured by using a
retaining ring 1.
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